The present invention relates to the fabrication of hard porous bodies particularly suitable as filter media for liquids and gases in highly oxidizing and thermally extreme environments which are prepared through the sintering together of metal particles. The preferred embodiment of the invention comprises the extrusion of metal particles into porous honeycomb structures that can perform as filters in the harshly corrosive exhaust stream of an internal combustion engine.
Porous ceramic bodies have been commercially exploited for a variety of industrial uses. For example, porous ceramic honeycomb structures have been employed to filter the exhaust stream of a diesel engine (U.S. Pat. No. 4,329,162). Whereas porous ceramic bodies continue to be a popular and useful material in such environments, there has been a desire to develop materials exhibiting greater mechanical strength, thermal resilience, and resistance to corrosion in highly oxidizing atmospheres. Because of the greater mechanical strength and resistance to thermal shock recognized as inherent in many metals, when compared to ceramic bodies, an investigation was undertaken to develop porous metal bodies capable of extended service in extremely hostile environments, especially in such highly oxidizing atmospheres as the exhaust stream of an internal combustion engine.
Stainless steel substrates are common to the internal combustion catalytic converter art. U.S. Pat. No. 3,788,486 suggests the use of sintered powder metal, generally, for use as porous filters. Disclosed is the use of austenitic stainless steel for use as a filter structure after being machined from a cylinder block; there is no mention of extruding a metal powder. U.S. Pat. No. 4,277,374 discloses the use of ferritic stainless steel which includes the addition of aluminum to improve the oxidation resistance of the porous substrate, with no mention of extrusion. U.S. Pat. No. 4,582,677 discloses the use of 100% pure aluminum, copper, titanium or zirconium metals as extrudable porous metallic honeycombs.
The prior art powdered metallic substrates suffer from either poor sinterability and/or mechanical strength, or they have poor corrosion resistance.
The primary object of the present invention is to overcome the deficiencies of the prior art and to provide a hard porous metal body which exhibits a mechanical strength typical of metals and is capable of enduring the thermal cycling and the oxidative corrosion inherent in the exhaust system of an internal combustion engine. The stability of the present inventive substrate body in highly corrosive environments invites its use in less corrosive environments as a substrate body with all of the above cited advantages.